Variations in Martian lithospheric strength based on gravity/topography analysis

Abstract

We applied localized gravity/topography admittance and correlation analysis, as well as the Markov chain Monte Carlo method, to invert for loading and flexural parameters of 21 subregions on Mars with five distinct tectonic types. The loading styles of the five tectonic types are distinct: The surface and subsurface loading in the polar and plain regions can be assumed to be largely uncorrelated, in contrast to the correlated loading associated with the volcanic montes and Valles Marineris. For the impact basins, we consider the initial topographic depression and mantle plug before postimpact surface loading. Our analyses yield four main results: (1) The inverted effective lithospheric thickness (Te) is highly dependent on assumptions of loading type. (2) There is a trend of increasing Te from the Noachian southern highlands (20–60 km) to the Hesperian northern lowlands (>90 km) and from the Hesperian Elysium Mons (<55 km) to the Hesperian/Amazonian Olympus Mons (>105 km). These Te estimates are consistent with the thermal states at the time of loading, corresponding to a global secular cooling history with decreasing heat flux. (3) Our analyses suggest high‐density basaltic surface loading at the volcanic montes and Isidis basin, in contrast to the low‐density sedimentary surface loading at the Utopia and Argyre basins. (4) We find some degree of correlation between the surface and subsurface loading for the northern polar cap and the northern plains, likely due to earlier, larger polar deposits and ancient buried features, respectively.